kernfs: implement kernfs_path_len()

Add a function to determine the path length of a kernfs node.  This
for now will be used by writeback tracepoint updates.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 2d48d28e1640..91e004518237 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -92,6 +92,29 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 }
 
 /**
+ * kernfs_path_len - determine the length of the full path of a given node
+ * @kn: kernfs_node of interest
+ *
+ * The returned length doesn't include the space for the terminating '\0'.
+ */
+size_t kernfs_path_len(struct kernfs_node *kn)
+{
+        size_t len = 0;
+        unsigned long flags;
+
+        spin_lock_irqsave(&kernfs_rename_lock, flags);
+
+        do {
+                len += strlen(kn->name) + 1;
+                kn = kn->parent;
+        } while (kn && kn->parent);
+
+        spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+
+        return len;
+}
+
+/**
  * kernfs_path - build full path of a given node
  * @kn: kernfs_node of interest
  * @buf: buffer to copy @kn's name into